Purification of an Exoribonuclease from Brain. An exoribonuclease from white matter, which has been purified about 300-fold, is being subjected to further purification. The enzyme is free RNase A, DNase, 2',3'-cyclic phosphodiesterase, 5'-nucleotidase, and acid and alkaline phosphatase activities. The enzyme release 3'-mononucleotides from the ends of the chains of natural and synthetic substrates, including homoribopolymer duplexes. Purification of 2',3'-Cyclic Nucleotide 3'-Phosphohydrolase. This myelin- associated, initially insoluble, enzyme has been purified about 50-fold after solubilization in 1 M guanidinium chloride in 0.05 MES buffer at pH 6, 10 to the minus 3 power M in EDTA and dithiothreitol. A key step in the purification is stepwise reduction of guanidinium chloride to permit removal by centrifugation of a fraction which apparently formed part of an insoluble complex in the tissue. The soluble enzyme thus obtained is being submitted to chromatographic fractionation. Fractionation of Brain Proteins. The procedure used to solublize the enzyme referred to in (2) above is being applied to a survey of insoluble, membrane-bound proteins in white matter, with the use of gel electrophoresis to monitor the fractionation and amino acid analysis of the protein from a single electrophoretic band for characterization.